I'm basically starting everything from scratch.

Soooo… About three years ago, I made some garbage Mary Sue characters in a heavily cliched universe. They were extremely overpowered and didn't have any personalities whatsoever, but little me absolutely loved them. I'd draw them, make up stories about them, joke about them, and even ship them (which, after fleshing out their characters and personalities… I still do).
Since they were so important to me back then, I figured maybe it would be a fun idea to turn those characters into something decent and then create a webcomic off of it. It sounded pretty simple at first since I already had multiple things to work from, but I discovered pretty quickly that it's just as difficult (if not more) to create a story with salvaged childhood OCs as it is to create one from scratch.

Well, after many messes, mistakes, and failures, I've decided to finally scrap everything but the "base ideas"/characters, build a solid backbone for the story, and then pile random ideas back on in the hopes that maybe, just maybe, I can finally create a story I don't feel embarrassed to speak of. However, I have no idea what to do now that I've got rid of all this. Do I work on the characters? Build up the few ideas I have? How do I build up those ideas? How do I create an actual plot? What about sub-plots? How should I know if an idea is good or bad? Am I overthinking things? I have so many questions

You might be wondering, "But Ella, why are you making a thread for people to help you if you have no idea what you need help with in the first place?" And my answer to that is:
I don't know. I just thought that maybe throwing my problems, ideas, and progress into a public thread would motivate me into making this decent so I don't embarrass myself in front of people. I do that enough already.

(NOTE: I will explain the "base ideas" and characters later, however, my WiFi's going off soon so I don't have time today. And by later, I mean I'll probably manage to completely forget about this and not say anything for a year.)

I'm here. And the first thing I have to say, is it what you have to do first, is come up with the premise. When you have that premise, explain it to me. Whether it's coming up with an entirely new one, or revamping your old one.

Hey! so I'm not in exactly the same position, but quite a similar one. I recently smashed a lot of my WIPs into one story and found that it didn't exactly work anymore, so I had to rework quite a bit for it to be coherent again.
I think where to start depends on how you prefer/want to create stories. In my case, my stories are very character-driven and I find that developing characters allows me to simultaneously develop the plot as their stories influence it. I only had the barest skeleton of a plot before I started working on characters whereas now it has a lot more nuance and subplots than it would if I'd just sat down and said "what needs to happen here?" and left it at that. For several of the characters, all that remained from their old WIP was "this character ends up in this situation at some point" so it was really fun to see how they get there and how that would affect everyone else in their world (I hope this makes any semblance of sense).
On the other hand, my story also happens in a different world. Worldbuilding the culture and environment also influences the plot as I realise that these things affect my plan and I adjust accordingly. For example, developing the standards of beauty for women was a little dumb thing I did a few months ago, but it shaped the way that some of my female characters structure their life around meeting those standards, which in turn affected the way they influence the story, if that makes sense.
So yeah - any progress is progress! Working on one thing rarely confines itself to affecting only one part of the story, so even doing the small thing that you've been meaning to do for a while can domino into bigger important points.
(another example because I'm still not sure I've explained this well - I sat down one day and decided to name two of my countries because I couldn't think of anything else to do. In the process, I decided that one of them was going to be named for its farmland, which ended up snowballing throughout my story and led to the plot point that literally kickstarts the entire premise (there are Food Riots and my mc is involved, basically). It doesn't have to work out like this, but I find it often does. Doing one tiny thing makes everything more coherent and you end up with more than you set out to accomplish)

sorry for the giant wall of text, I got carried away

Going off of that, I find that developing characters really does help to shape the world you're trying to create. Someone's a blacksmith? Alright, why? Is it important? Is it a passion? A hobby? Do they sell to anyone? Anyone important? Coming up with stories like these create smaller narratives that the reader will become invested in, and I feel like it's all one big Dungeons & Dragons game.
Everyone has their own motives, and it's up to the DM (the author, you, in this case) to weave all of their motives together and figure out "What do they want?" "When do they want it?" and "How can I prevent them from getting it?"

Thank you guys so much!

You could just start writing. When I started my book, I did it on a whim. I had no idea where the story was going to go, but as I wrote, more and more ideas came to me. This method is called pantsing, and I'm pretty sure that it's going to require intense editing for the second draft, but it is a legitimate writing method. If you would prefer to have a basic outline of the story first though, here is what I would suggest. First, find something you want to say. Think of something that frustrates you or a belief that you want to express. Having a coherent non-generic theme is going to greatly help you come up with ideas for the story. Try thinking of the themes for your favorite films if you need examples. The next thing I would suggest is to figure out the genre of your story. Then the setting, is it set in modern day, the past, the future? You can fill in the details later, but first, try to find the basics.
The first line of any book, the first scene of any movie, and the first panel of any comic should grab the reader's interest. The first few pages should let the reader know what TYPE of story this is going to be, or give the reader some indication of where the story is headed. The first scene of the Captain America movie shows him being discovered frozen in ice inside of a crashed plane. This interests the audience and makes them want to keep watching so as to see how this happened to this man. The second scene of the movie shows the tesseract being stolen. This lets the audience know that this is going to be a sci-fi film. If these two scenes weren't in the film, and the movie just began with the third scene which is of Steve being beaten up in the alley after telling the rude man in the audience to shut up, it would have still probably been a highly rated movie, but it would have lost the thing that makes audiences want to watch till the end as well as losing the set up for the sci-fi component. The audience might have assumed that this was just a ww2 drama film, which would have made the super soldier serum and tesseract thing really jolting because they aren't really mentioned again until quite a ways into the movie.

Wow, Hannah, excellent advice! That might legitimately